It is 1(am/pm) It common to leave out the o'clock or am/pm when there is no ambiguity when speaking. For example, When's the next match? It's at 2. Based on the current time the two speakers can infer the am/pm. However, saying It's 2 by itself is uncommon: the o'clock is needed to specify that the current time is 2. Usage For business documents More @Wikipedia
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